Add field descriptors that include display name, sort order, isHidden, isLink, linkText that can be edited in the UI for each dataset.

[dylanett]

• flag aggregatable fields

Usage suggestions from Paul:

• Put ItemID (labelled as Census ItemID) and Geo_Site in the first two columns if present.
• Put any link columns at the end.
• Don't include both identical columns such as "href jpg" and "src jpg"
• Use better human readable column headings, such as Facsimile JPG instead of href jpg.